mozilla-2.0 branch, and changes in binary compatibility policies: The branch from which FF4 will be delivered will be called "mozilla-2.0", with a Gecko version of 2.0. Along with this change, we will be moving to a narrower set of binary (native code) compatibility promises for future releases. A quick summary:

Between micro/maintenance releases, such as 2.0.1 to 2.0.2, our policy remains unchanged: no incompatible changes to native-code interfaces except as a last resort when predicated by a security requirement.

Between minor or major releases, such as 2.0.x to 2.1.x or 1.9.x to 2.0.x, native-code interface compatibility is not guaranteed, even for interfaces that were previously considered FROZEN: providers of native code components, and embedders who use native-code interfaces, will at least need to recompile. We will endeavour to provide a smooth migration strategy for cases where source compatibility is not feasible, and we will also work to ensure that extension authors which rely on native components can support at least two adjacent incompatible Gecko versions in the same package.

JSAPI, NSPR, NSS and other currently-linkable libraries may disappear into libxul, and extension authors should avoid linking against them. XPCOM and interfaces expressed in XPCOM will continue to be available, subject to the above; specific interfaces may change between minor or major versions, including changes in semantics as well as implementation details.

Scripted interface compatibility with the platform will be maintained aggressively, though we recommend that, for Firefox 4 and beyond, extension authors use the Jetpack APIs where feasible. (Where not feasible, please submit a JEP!)

JS-ctypes is the recommended way to interface between extension JS code and custom or OS-provided native code.

If anyone can lend a hand with reviewing these, that would save Dão and other very busy reviewers some work. If these don't get reviewed and landed by tomorrow, Mac beta 1 will ship without any UI updates, which would make everyone sad. (contact limi or shorlander if you want to help!)

GFX/Hardware Acceleration Update

Hope to turn Direct2D by default soon without regressing startup by too much (minimal for those without sufficient hardware, ~130ms? for those with)

Support for accelerated, full-screen video on linux just landed, please give it a try.

Layout Update

Should drop retained layers for beta1: too much risk, still probably a few days away at best